linux-kernel - Re: [PATCH v6] taskstats: fix data-race

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Message-ID: <CACT4Y+ZXQyqgBvwgb6cy7NP5FTBbktq5j4ZyySp7jrbcJwFUTA@mail.gmail.com>
Date:   Thu, 24 Oct 2019 15:58:40 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Andrea Parri <parri.andrea@...il.com>
Cc:     Christian Brauner <christian.brauner@...ntu.com>,
        Will Deacon <will@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>, bsingharora@...il.com,
        Marco Elver <elver@...gle.com>,
        stable <stable@...r.kernel.org>,
        syzbot <syzbot+c5d03165a1bd1dead0c1@...kaller.appspotmail.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>
Subject: Re: [PATCH v6] taskstats: fix data-race

On Thu, Oct 24, 2019 at 3:43 PM Andrea Parri <parri.andrea@...il.com> wrote:
>
> > But why? I think kernel contains lots of such cases and it seems to be
> > officially documented by the LKMM:
> > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/memory-model/Documentation/explanation.txt
> > address dependencies and ppo
>
> Well, that same documentation also alerts about some of the pitfalls
> developers can incur while relying on dependencies.  I'm sure you're
> more than aware of some of the debate surrounding these issues.

I thought that LKMM is finally supposed to stop all these
centi-threads around subtle details of ordering. And not we finally
have it. And it says that using address-dependencies is legal. And you
are one of the authors. And now you are arguing here that we better
not use it :) Can we have some black/white yes/no for code correctness
reflected in LKMM please :) If we are banning address dependencies,
don't we need to fix all of rcu uses?